System and method for controlled mixing of fluids

ABSTRACT

Embodiments of the present invention provide a system and method for continuous flow production of mixed fluids. The mixed fluids can comprise a mixture of different fluids or a mixture of the same fluid having different input properties such as temperature. In general, two streams of fluid of varying temperature are supplied to a mixer. The flow rate of each of the input fluids can be regulated to produce a mixed fluid at a desired flow rate and temperature. As an example, mass flow controllers can regulate the flow rates of a hot and cold stream of de-ionized water to produce a stream of de-ionized water at a desired flow rate and temperature.

RELATED APPLICATIONS

This application is a divisional of and claims priority under 35 U.S.C.§120 to U.S. patent application Ser. No. 11/365,395, entitled “SYSTEMAND METHOD FOR MULTIPLEXING SETPOINTS”, by McLoughlin, filed Mar. 1,2006, which is hereby fully incorporated by reference herein.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to chemical delivery systems. Moreparticularly, embodiments of the present invention relate to systems andmethods for the controlled mixing of fluids.

BACKGROUND

Controlled composition fluids are present in a number of widely usedfluids including municipal water supplies, beverages, gasoline,intravenous (“IV”) fluids and other useful fluids. In some cases, thecontrolled composition fluid is not the end product of a process, but isused in the manufacturing process of other products. For example,semiconductor manufacturing processes commonly use controlledcomposition fluids in cleaning and etching of semiconductor wafers.

Systems for creating controlled composition fluids typically mix anumber of constituent fluids according to a proscribed ratiometriccombination-in other words, a recipe. In some cases, it is not thestochiometric ratio of the fluid components that is important, but someproperty of the fluid mixture, such as pH, viscosity, ionic strength,conductivity or other property. Rather than controlling for thepreferred property, however, it is often easier to blend the fluidcomponents to a target concentration which corresponds to the actualtarget property.

Typically, fluids of a particular concentration are produced in a batchmode. In a batch process, the gravimetric or volumetric ratios ofcomponent fluids are used to determine how much of each fluid is addedinto a mix vessel for blending. While the use of batch process allowsfor fairly easy control of concentration, it limits production of theblended fluid to a particular size batch. To provide additional blendedfluid, more batches of the fluid must be produced. Additionally, currentbatch process systems have large footprints, relatively high capitalcosts and a high level of complexity. Examples of batch systems includeChemFlow Systems, Inc. of Addison, Ill. batch system which blendsgravity fed components volumetrically, and the MassFusion™ system by BOCEdwards.

In addition to batch processes, controlled composition fluids can alsobe produced using continuous flow systems that mix fluids as the fluidsflow to the process chamber. These systems provide for continuousproduction of a fluid. Currently continuous flow systems do not provideadequate control to compensate for inaccurate or changing componentfluid properties such as concentration or temperature.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a system and method ofcontinuous mixing of fluids that eliminates, or at least substantiallyreduces, the shortcomings of prior art fluid mixing systems and methods.More particularly, embodiments of the present invention provide a systemand method to provide a mixed fluid at a desired flow rate andtemperature in a manner that can quickly adjust for changing processparameters.

One embodiment of the present invention includes a fluid mixing systemcomprising a first flow controller (e.g., a cold fluid flow controller)to control the flow of a first fluid, a second flow controller (e.g., ahot fluid flow controller) to control the flow a second fluid, a firstmixer (e.g., a static mixer) in fluid communication with and downstreamof the first flow controller and second flow controller to mix the firstand second fluid to produce a first mixed fluid and a temperature sensordownstream of the first mixer to measure the temperature of the firstmixed fluid. The first flow controller is configured to regulate theflow of the first fluid using a desired flow rate for the first fluidwhile the second flow controller is configured to regulate the flow ofthe second fluid based on a temperature setpoint and temperature of thefirst mixed fluid.

Another embodiment of the present invention includes a fluid mixingmethod comprising providing a first fluid and second fluid to a firstmixer, mixing the first fluid and second fluid at the first mixer tocreate a first mixed fluid, measuring the temperature of the first mixedfluid, regulating the flow of the first fluid to the mixer based on afirst fluid target flow rate and regulating the flow of the second fluidto the mixer based on the temperature of the first mixed fluid and atemperature setpoint.

Yet another embodiment of the present invention includes a fluid mixingsystem comprising a hot fluid flow controller to control the flow of ahot fluid, a cold fluid flow controller to control the flow of a coldfluid, a first static mixer downstream of the first hot fluid flowcontroller and the cold fluid flow controller to receive the hot fluid,receive the cold fluid and mix the hot and cold fluids to create a mixedfluid, a mixed fluid temperature sensor to determine the temperature ofthe mixed fluid, a chemical flow controller to control the flow of achemical, a second static mixer downstream of the chemical flowcontroller and the first static mixer to mix the mixed fluid and thechemical to create a dilute chemical and a chemical temperature sensorto measure the temperature of the dilute chemical. According to oneembodiment, the cold fluid flow controller controls the flow of the coldfluid based on a cold fluid target flow rate and communicates atemperature setpoint to the hot fluid flow controller. The hot fluidflow controller regulates the flow rate of the hot fluid based on thetemperature setpoint and temperature of the mixed fluid. The temperaturesetpoint can be continually updated based on the temperature of thedilute chemical. The chemical flow controller controls the flow of thechemical based on a target chemical flow rate.

The present invention provides an advantage over prior art systems andmethods of mixing fluids by providing the ability to adjust temperature,chemistry and flow rate on the fly, leading to increased throughput andprocess flexibility.

Embodiments of the present invention provide another advantage overprior art systems of mixing fluids by providing the ability to rapidlycompensate for changes in component fluid properties such asconcentration, temperature and other process parameters.

In addition, embodiments of the present invention provide anotheradvantage over prior art systems by controlling a hot fluid using atemperature based flow controller, thereby reducing errors that hightemperatures caused by higher temperatures in pressure based flowcontrollers.

BRIEF DESCRIPTION OF THE FIGURES

A more complete understanding of the present invention and theadvantages thereof may be acquired by referring to the followingdescription, taken in conjunction with the accompanying drawings inwhich like reference numbers indicate like features and wherein:

FIG. 1 is a diagrammatic representation of one embodiment of a systemfor mixing fluids;

FIGS. 2A and 2B provide flow charts illustrating one embodiment of amethod for controlling flow of fluids to create a mixed fluid;

FIG. 3 is a diagrammatic representation of another embodiment of asystem for mixing fluids;

FIGS. 4A-4C provide flow charts illustrating one embodiment of anothermethod for controlling flow of fluids to create a mixed chemical;

FIG. 5 is a diagrammatic representation of yet another embodiment ofsystem for mixing fluids;

FIGS. 6A-6C provide flow charts illustrating another embodiment ofanother method for controlling flow of fluids to create a mixedchemical;

FIGS. 7A-7F provide diagrammatic representations of one embodiment of astatic mixer assembly 700 and its components;

FIGS. 8A-8C provide diagrammatic representations of another embodimentof a mixer assembly;

FIG. 9 is a diagrammatic representation of one embodiment of a systemfor multiplexing analog set points;

FIG. 10 is a diagrammatic representation of an analog setpoint signaland corresponding setpoint indicator signals;

FIG. 11 is a diagrammatic representation of one embodiment of a systemfor multiplexing analog setpoints;

FIG. 12 is a diagrammatic representation of an analog setpoint signaland corresponding signals for asserting setpoint indicators; and

FIG. 13 is a flow chart illustrating one embodiment of multiplexinganalog setpoints.

DETAILED DESCRIPTION

Preferred embodiments of the invention are illustrated in the FIGURES,like numerals being used to refer to like and corresponding parts of thevarious drawings.

Embodiments of the present invention provide a system and method forcontinuous flow production of mixed fluids. The mixed fluids cancomprise a mixture of different fluids or a mixture of the same fluidhaving different input properties such as temperature. In general, twostreams of fluid of varying temperature are supplied to a mixer. Theflow rate of each of the input fluids can be regulated to produce amixed fluid at a desired flow rate and temperature. As an example, massflow controllers can regulate the flow rates of a hot and cold stream ofde-ionized water (D.I. H₂O or DIW) to produce a stream of D.I. H₂O at adesired flow rate and temperature.

The control algorithm of the mass flow controllers can rely on the factthat only one combination of mass flow rates of particular input fluidswill produce a mixed fluid at the desired temperature and flow rate.Consequently, one of the mass flow controllers, acting as a mastercontroller, can calculate the desired flow rate of fluid through itbased on the temperatures of the input fluids, the specific heat(s) anddensities of the input fluids, the target flow rate of the mixed fluidand the target temperature of the mixed fluid. The master controller canthen pass the target temperature to a slave mass flow controller. Theslave mass flow controller adjusts the flow rate of fluid through itbased on the target temperature and the temperature of the mixed fluidas determined by a temperature sensor.

By using a temperature sensor to create a feedback loop to the slavemass flow controller, the slave mass flow controller can regulate fluidflow rate to quickly bring the mixed fluid to the desired temperature.As the temperature of the mixed fluid approaches the desiredtemperature, the flow rate of fluid through the slave mass flowcontroller is adjusted such that the flow rate of the mixed fluidapproaches the desired flow rate. Thus, the mixed fluid will reach thedesired temperature and flow rate.

FIG. 1 is a diagrammatic representation of one embodiment of a system100 for mixing fluids. System 100 includes two flow controllers 102 and104 that are in fluid communication with a mixer 106. System 100 furtherincludes a temperature sensor 108 upstream of flow controller 102, atemperature sensor 110 upstream of flow controller 104 and a temperaturesensor 112 downstream of mixer 106. Temperature sensor 108 andtemperature sensor 110 are connected to (i.e., can communicate a signalrepresentative of temperature) at least one of the flow controllers;flow controller 104 in this example. Temperature sensor 112 is alsoconnected to at least one of the flow controllers. In this example,temperature sensor 112 is connected to flow controller 102.

According to one embodiment, flow controller 102 and flow controller 104is each an OptiChem P1200 LFC flow controller produced by MykrolisCorporation of Billerica, Mass. (now part of Entegris, Inc. of Chaska,Minn.), though other suitable flow controllers can be utilized. Mixer106 can include any suitable dynamic or static mixer for mixing fluidflows. One embodiment of a static mixer is described in conjunction withFIGS. 7A-7F. The temperature sensors 108, 110 and 112 can include anysuitable temperature sensors.

Fluid that is hotter than a target temperature (e.g., hot fluid 114) issupplied to flow controller 102 and a fluid that is colder than a targettemperature (e.g., cold fluid 116) is supplied to flow controller 104.Flow controller 102 regulates the flow of hot fluid 114 and flowcontroller 104 regulates the flow of cold fluid 116 to mixer 106. Thesefluids are blended at mixer 106 to produce mixed fluid 118 at a desiredtemperature and flow rate.

The flow rates of hot fluid 114 and cold fluid 116 to mixer 106 can becontrolled based on a target temperature (e.g., of mixed fluid 118), thetemperatures of the hot and cold fluids, the fluid properties of the hotand cold fluids and the measured temperature of mixed fluid 118. Moreparticularly, a process tool, control computer or other system canprovide flow controller 104 a target temperature (t_(T1)) and flow rate(Q_(T1)) of mixed fluid 118. Additionally, temperature sensor 108provides the temperature of hot fluid 114 (t_(H)) and temperature sensor110 provides the temperature of cold fluid 116 (t_(c)). Flow controller102 and flow controller 104 can also be provided with or preprogrammedwith the type of hot and/or cold fluid used in system 100.

Based on the fluid type and temperatures of hot fluid 114 and cold fluid116, flow controller 102 can calculate the densities (ρ_(H), ρ_(c)) andspecific heats (Cp_(H), Cp_(C)) of hot fluid 114 and cold fluid 116.Flow controller 104 can similarly determine the density (p_(T)) andspecific heat (Cp_(T)) of mixed fluid 118 at the target temperature(t_(T)). For example, if each of hot fluid 114 and cold fluid 116 isD.I. H₂O, the densities and specific heats can be calculated based onpolynomials using the following coefficients: TABLE 1 Order ρ = f (t) Cp= f (t) 0  .99988  1.00919 1  6.20242E−05 −9.50319E−04 2 −8.37727E−06 2.8655E−05 3  6.62195E−08 −4.28993E−07 4 −4.17404E−10  3.44932E−09 5 1.15955E−12 −1.10643E−11

Table 1 is provided by way of example and not limitation. Otherequations, lookup tables or other suitable mechanism can be used todetermine the specific heat and density for hot fluid 114, cold fluid116 and mixed fluid 118. Moreover, it should be understood that hotfluid 114 and cold fluid 116 can be different fluids.

Using the target flow rate (Q_(T1)), target temperature (t_(T1)), hotfluid temperature (t_(H)), cold fluid temperature (t_(c)), specificheats of the hot, cold and mixed fluids (Cp_(H), Cp_(C), Cp_(T)) anddensities of the hot and cold fluids (p_(H), p_(C)), controller 104,according to one embodiment, can calculate the target flow rate of coldfluid 116 (Q_(C)) to mixer 106 based, for example, on the followingequation:Q _(C) =Q _(T)*(1000/60)*(ρ_(C)/ρ_(T))*(t _(H) *Cp _(H) −t _(T) Cp_(T))/(t _(H) *Cp _(H) −t _(C) *Cp _(C))  [EQN. 1] Q_(T) = target flowrate (lpm) t_(T) = target temperature (° C.) t_(H) = hot fluidtemperature (° C.) t_(C) = cold fluid temperature (° C.) ρ_(C) = coldfluid density (g/cm³) ρ_(H) = hot fluid density (g/cm³) Cp_(C) = coldfluid specific heat (cal/g*° C.) Cp_(H) = hot fluid specific heat(cal/g*° C.) Cp_(T) = mixed fluid specific heat at t_(T) (cal/g*° C.)

Continuing with the previous example, Q_(T)=Q_(T1) and t_(T)=t_(T1), andflow controller 104 can determine the appropriate Q_(C) according to anymechanism known or developed in the art. Flow controller 104 canregulate the flow of cold fluid 116 to the rate of Q_(C) (within thetolerances of flow controller 104) using pressure differential basedflow control, heat loss based flow control or other flow control scheme.

Flow controller 104 can further pass a temperature set point t_(SP) tocontroller 102. The temperature set point, in this case, can indicatethe desired temperature of mixed fluid 118. For example, t_(SP) can beequal to t_(T). Controller 102 compares the temperature of the mixedfluid (t_(M1)) to t_(SP). If t_(M1)>than t_(SP), controller 104 candecrease the flow of hot fluid 114 and if t_(M1)<t_(SP), controller 104can increase the flow of hot fluid 114. By adjusting the flow of hotfluid, t_(M1) will approach t_(SP). When t_(M1) is approximately equalto t_(SP), (i.e., within an acceptable deviation (e.g. 5%)), thisindicates that mixed fluid 118 has reached the target flow rate andtarget temperature. In another embodiment, flow controller 104 receivest_(M1) from temperature sensor 112 and passes t_(M1) and t_(SP) to flowcontroller 102.

Controller 104 can continually recalculate Q_(C) and t_(SP) (e.g.,approximately at 1 Hz or above, according to one embodiment) as theinput fluid temperatures, desired mixed fluid flow rate or otherparameters change. Thus, the present invention can quickly adjust tochanging process parameters.

As described above, controller 104 and controller 102 act in amaster-slave fashion with controller 104 providing t_(SP) to controller102. The master-slave dynamic of these controllers can be reversed withcontroller 102 processing the inputs providing a t_(SP) to controller104. Furthermore, one of the controllers can be provided with the targettemperature and flow rate and the other controller can be provided witht_(SP) from an outside computer system or tool. In this case, neithercontroller 102 nor controller 104 acts as a master or slave with respectto the other controller.

It should be noted that higher temperature fluids can cause errors inpressure based controllers. If a pressure based flow controller is usedto control the hot DIW, significant errors may be encountered ascommonly used pressure sensors are typically sensitive to temperaturechanges. If the hot fluid flow controller controls flow based onpressure, temperature compensation circuitry can be used. Or, as in theembodiments described above, the hot fluid flow controller can employ atemperature based control scheme.

FIGS. 2A and 2B provide flow charts illustrating one embodiment of amethod for controlling flow of fluids to create a mixed fluid. Themethod of FIGS. 2A and 2B can be implemented as computer instructionsthat are executable by a processor stored on a computer readable medium.For example, embodiments of the present invention can be implementedthrough programming of one or more OptiChem P1200 LFC flow controllers.

The flow chart of FIG. 2A corresponds to the control method implementedat the cold fluid flow controller (e.g., flow controller 104 of FIG. 1)and FIG. 2B corresponds to the method implemented at the hot fluid flowcontroller (e.g., flow controller 102 of FIG. 1).

The cold fluid flow controller receives inputs including the targetmixed fluid temperature (t_(T1)), the target mixed fluid flow rate(Q_(T1)), the cold fluid temperature (t_(C)), the hot fluid temperature(t_(H)) (step 202). Using these inputs and the properties such asspecific heat and density of the cold fluid, hot fluid and mixed fluid(at the target temperature), the cold fluid flow controller calculatesthe cold fluid flow rate (Q_(C)) according to EQN. 1, where Q_(T)=Q_(T1)and t_(T)=t_(T1) (step 204). The cold fluid flow controller sets atemperature set point t_(SP) for the hot fluid flow controller (step206). For example, t_(SP) can be calculated or set to t_(T1).

When a trigger signal is received (step 208), the cold fluid flowcontroller can begin regulating fluid flow using Q_(C) as a flow rateset point and issue commands the hot fluid flow controller to regulateflow of the hot fluid (step 210). The cold fluid flow controller canadjust the flow of cold fluid according to fluid flow control schemesknown in the art, including but not limited to differential controlschemes, integral control schemes, proportional integral controlschemes, fuzzy logic or proportional integral differential controlschemes. If the fluid flow of cold water is greater than the fluid flowset point, cold fluid flow controller can decrease the flow rate (step212), if the fluid flow of cold water is less than the fluid flow setpoint, the cold fluid flow controller can increase the flow rate, and ifthe cold fluid flow rate equals the set point (within an acceptablesystem tolerance) (step 214), the cold fluid flow controller canmaintain the flow rate (step 216). Thus, the cold fluid flow controllercan adjust the flow rate of cold fluid based on the target cold fluidflow rate set point Q_(C).

Turning to FIG. 2B, the hot fluid flow controller, on the other hand,can adjust the flow rate of the hot fluid based on the temperature ofthe mixed fluid (t_(M1)) and the mixed fluid set point (t_(SP)). Thetemperature of the mixed fluid can be received either directly from atemperature sensor or from the cold fluid flow controller. If t_(M1) isgreater than t_(SP), the hot fluid flow controller decreases the flowrate of fluid (step 218), if t_(M1) is less than t_(SP), the hot fluidflow controller increases the flow rate of the hot fluid (step 220) andif t_(M1) is equal to t_(SP) (within acceptable system tolerances), thehot fluid flow controller maintains the flow rate of hot fluid (step222).

The steps of FIGS. 2A and 2B can be repeated as needed or desired.Moreover, the various steps can be performed in a variety of orders andvarious steps performed by each flow controller can be performed inparallel.

While, in the embodiment of FIGS. 2A and 2B, the cold water flowcontroller is responsible for determining the set point t_(SP) for thehot water flow controller, in other embodiments, the hot water flowcontroller can determine t_(SP) for itself or provide t_(SP) to the coldwater flow controller so that the cold water flow controller canregulate flow based on t_(M). In other words, the roles of the hot andcold water flow controllers can be reversed and the steps of FIG. 2 canbe otherwise distributed between the controllers.

Thus, one embodiment of the present invention can include a first flowcontroller (e.g. flow controller 104), a second flow controller (e.g.flow controller 102) and a mixer downstream of the first and second flowcontrollers. The first flow controller can regulate the flow of a firstfluid based on a target flow rate for the first fluid (e.g., Q_(C)), andthe second flow controller can regulate the flow of a second fluid basedon a temperature set point and a temperature of the mixed fluid createdby the mixer.

The system of FIG. 1 can be implemented as a subsystem of a largermixing system that combines the mixed fluid with additional fluids, suchas other chemicals. FIG. 3 illustrates a solution mixing system 300 thatincorporates the subsystem of FIG. 1. In the example of FIG. 3, solutionmixing system 300 provides a concentrated NaCl solution mixing system inwhich the mixed DIW 118 is combined with NaCl to produce dilute NaCl302. In addition to the components discussed in conjunction with FIG. 1,solution mixing system 300 includes one or more sources of concentratedNaCl (here illustrated as 1800 parts per million (ppm) NaCl source 304,2000 ppm source 306 and 2200 ppm source 308). A chemical flow controller310 controls the flow of concentrated NaCl to a second mixer 312 wherethe concentrated chemical is mixed with mixed DIW 118. Mixer 312,according to one embodiment of the present invention can be a staticmixer.

For the sake of example, cold fluid flow controller 104 can act as amaster controller for hot fluid flow controller 102 and chemical flowcontroller 310. Cold fluid flow controller 104 receives a target mixedchemical flow rate (Q_(T2)) for dilute NaCl 302, a target mixed chemicalratio for dilute NaCl, a target mixed chemical temperature (t_(T2)) fordilute NaCl 302, t_(C), and t_(H). Based on the target mixed chemicalflow rate Q_(T2) and the target mixed chemical ratio, cold fluidcontroller 104 can determine the target flow rate of DIW (Q_(T1)) andflow rate of concentrated NaCl (Q_(chem)). Assuming that the temperatureof the concentrated chemical has a negligible effect on the temperatureof dilute NaCl 302, the target temperature of mixed DIW 118 can be setequal to t_(T2) (i.e., t_(T1)=t_(T2)). Using t_(T2), Q_(T1) and theinput temperatures of the hot and cold DIW, cold fluid flow controller104 can further determine the target cold DIW flow rate (Q_(C)) andtemperature set point t_(SP) for hot fluid flow controller 104. Coldfluid flow controller 104 provides t_(SP) to hot fluid flow controller102 and Q_(chem) to chemical flow controller 310. Each flow controllercan then control the flow of its respective fluid.

FIGS. 4A-4C are flow charts illustrating one embodiment of a method forcontrolling flow of fluids to create a mixed fluid. The method of FIGS.4A-4C can be implemented as computer instructions that are executable bya processor stored on a computer readable medium. For example,embodiments of the present invention can be implemented throughprogramming of one or more OptiChem P1200 LFC flow controllers.

FIG. 4A corresponds to the control method implemented at the cold fluidflow controller (e.g., flow controller 104 of FIG. 3), FIG. 4Bcorresponds to the control method implemented at the hot fluid flowcontroller (e.g., flow controller 102 of FIG. 3) and FIG. 4C to thecontrol method implemented at chemical flow controller 310.

The cold fluid flow controller receives inputs including the targetmixed chemical mix ratio, the target mixed chemical flow rate (Q_(T2)),the cold fluid temperature (t_(C)), the hot fluid temperature (t_(H)),the target mixed chemical temperature (t_(T2)) (step 402). Using thetarget mixed chemical mix ratio and the target mixed chemical flow rateQ_(T2), the cold fluid flow controller can determine the target DIW flowrate Q_(T1) and the flow rate of the concentrated chemical or otherfluid (Q_(chem)) (e.g., NaCl in the example of FIG. 3) (step 406).Assuming that the flow of NaCl will have little effect on the overalltemperature of the mixed chemical, the cold fluid flow controller canset the target mixed DIW temperature (t_(T1)) equal to the target mixedchemical temperature (t_(T2)) and determine Q_(C) according to EQN 1,where Q_(T)=Q_(T1) (step 408). Additionally, the cold fluid flowcontroller can set t_(SP)=t_(T1)=t_(T2) (also shown at 409).

When a trigger signal is received (step 410), the cold fluid flowcontroller can begin regulating fluid flow using Q_(C) as a flow rateset point, issue commands to the hot fluid flow controller to regulateflow of the hot fluid and issue commands to the chemical flow controllerto control flow of the third fluid. The cold fluid flow controller canfor adjust the flow of cold fluid according to fluid flow controlschemes known in the art, including but not limited to differentialcontrol schemes, integral control schemes, proportional integral controlschemes, fuzzy logic or proportional integral differential controlschemes. If the fluid flow of cold water is greater than the fluid flowset point, cold fluid flow controller can decrease the flow rate (step412), if the fluid flow of cold water is less than the fluid flow setpoint (step 414), the cold fluid flow controller can increase the flowrate, and if the cold fluid flow rate equals the set point (within anacceptable system tolerance), the cold fluid flow controller canmaintain the flow rate (step 416). Thus, the cold fluid flow controllercan adjust the flow rate of cold fluid based on the cold fluid flow rateset point Q_(C).

As shown in FIG. 4B, the hot fluid flow controller can adjust the flowrate of the hot fluid based on the temperature of the mixed fluid(t_(M1)) and the mixed fluid set point (t_(SP)). The temperature of themixed fluid can be received either directly from a temperature sensor orfrom the cold fluid flow controller. If t_(M1) is greater than t_(SP),the hot fluid flow controller decreases the flow rate of fluid (step418), if t_(M1) is less than t_(SP), the hot fluid flow controllerincreases the flow rate of the hot fluid (step 420) and if t_(M1) isequal to t_(SP) (within acceptable system tolerances), the hot fluidflow controller maintains the flow rate of hot fluid (step 422).

The chemical flow controller can similarly adjust the flow of theadditional fluid (e.g., concentrated NaCl) based on Q_(chem) as is shownin FIG. 4C. If the fluid flow of the concentrated chemical (or otherfluid) is greater than the Q_(chem), chemical flow controller candecrease the flow rate (step 428), if the fluid flow of the concentratedchemical is less than Q_(chem) (step 430), the cold fluid flowcontroller can increase the flow rate, and if the concentrated chemicalflow rate equals the set point (within an acceptable system tolerance),the chemical flow controller can maintain the flow rate (step 434).Thus, the chemical flow controller can adjust the flow rate ofconcentrated chemical based on the cold fluid flow rate set pointQ_(chem).

The flow charts of FIGS. 4A-4C represent one example embodiment of thepresent invention. However, it should be understood, that the steps ofFIGS. 4A-4C can be repeated as needed or desired and can be performed indifferent orders. Moreover, the steps implemented at each flowcontroller can be performed in parallel. While, in FIGS. 4A-4C, the coldwater flow controller is responsible for calculating various parametersand asserting set points to the hot water flow controller and chemicalflow controller, the step of FIGS. 4A-4C can be otherwise distributed tothe flow controllers. Additionally, the roles of the hot water and coldwater flow controllers can be reversed such that the hot water flowcontroller controls flow based on a flow rate set point and the coldwater flow controller controls flow based on a temperature set point.

In the embodiment of FIGS. 3 and 4A-4C, it is assumed that t_(T2) is notgreatly affected by the temperature of the additional fluid added at thesecond mixer 312. Thus, it is assumed that the temperature of fluid atthe outlet of mixer 312 (t_(M2)) is approximately t_(M1) (i.e., isapproximately the temperature of the mixed DIW). According to anotherembodiment of the present invention, an additional temperature sensorcan be used to measure t_(M2) so that this temperature can be used inflow control.

FIG. 5 is a diagrammatic representation of one embodiment of a solutionmixing system 500 similar to that of FIG. 3 that adds a conductivitymeter 502 and an additional temperature sensor 504 downstream of secondmixer 312. Because the conductivity of a fluid is typically related tothe concentration of a fluid, the feedback from conductivity sensor 502can be used to adjust the concentration of concentrated chemical addedat static mixer 312 to achieve a desired conductivity. Additionally, thetemperature read by temperature sensor 504 can be used to adjust theflow rates of the hot and cold DIW.

For the sake of example, cold fluid flow controller 104 can act as amaster controller for hot fluid flow controller 102 and chemical flowcontroller 310. Initially, cold fluid flow controller 104 receives atarget mixed chemical flow rate (Q_(T2)), a target mixed chemical ratio,a target mixed chemical temperature (t_(T2)), t_(C), and t_(H). Based onthe target mixed chemical flow rate Q_(T2) and the target mixed chemicalratio, cold fluid controller 104 can determine the target flow rate ofDIW (Q_(T1)) and flow rate of concentrated NaCl (Q_(chem)). Initially,t_(T1) can be set equal to t_(T2). Using Q_(T1), t_(T2), and the inputtemperatures of the hot and cold DIW, cold fluid flow controller 104 canfurther determine the target cold DIW flow rate (Q_(C)) and temperatureset point t_(SP) for hot fluid flow controller 104. t_(SP) can alsoinitially be set equal to t_(T2). Cold fluid flow controller 104provides t_(SP) to hot fluid flow controller 102 and Q_(chem) tochemical flow controller 310. Each flow controller can then control theflow of its respective fluid.

According to one embodiment, controller 104 can use the temperature ofthe dilute chemical (t_(M2)) to adjust the flow rates of hot and coldDIW. Although control using t_(M2) can begin immediately, according toother embodiments, cold fluid flow controller 104 can wait a predefinedperiod of time before beginning control using t_(M2). This can be done,for example, to allow the flow and temperature of the dilute chemical tosettle.

Cold fluid flow controller 104, according to one embodiment, can adjustQ_(C) and t_(SP) based on the measured temperature of the mixed chemical(t_(M2)). For example, given t_(M2) from temperature sensor 504, coldfluid flow controller 104 can set the new t_(SP) equal to:t _(SP(n)) =t _(SP(n−1))+(t _(T2) −t _(M2))  [EQN. 2]

Thus, if t_(M2) is greater than t_(T2), the t_(SP) is lowered, leadingto a decrease in the temperature of DIW, and if t_(M2) is less thant_(T2), t_(SP) is raised, leading to an increase in the temperature ofDIW. Cold fluid flow controller 104 can further determine a new targetflow rate for the cold DIW (i.e., a new Q_(C)) using the t_(SP)calculated in EQN 2 for t_(T) of EQN 1. As described above, cold fluidflow controller 104 can regulate flow according to Q_(C) and hot fluidflow controller 102 can regulate flow according to t_(SP) and t_(M1).

FIGS. 6A-6C are flow charts illustrating one embodiment of a method forcontrolling flow of fluids to create a mixed fluid. The method of FIGS.6A-6C can be implemented as computer instructions that are executable bya processor stored on a computer readable medium. For example,embodiments of the present invention can be implemented throughprogramming of one or more OptiChem P1200 LFC flow controllers.

FIG. 6A corresponds to the control method implemented at the cold fluidflow controller (e.g., flow controller 104 of FIG. 5), FIG. 6Bcorresponds to the control method implemented at the hot fluid flowcontroller (e.g., flow controller 102 of FIG. 5) and FIG. 6C correspondsto the control method implemented at chemical flow controller 310.

The cold fluid flow controller receives inputs including target mixedchemical mix ratio, the target mixed chemical flow rate (Q_(T2)), thecold fluid temperature (t_(C)), the hot fluid temperature (t_(H)), thetarget mixed chemical temperature (t_(T2)) (step 602). Using the targetmixed chemical mix ratio and the target mixed chemical flow rate Q_(T2),the cold fluid flow controller can determine the target DIW flow rateQ_(T1) and the flow rate of the concentrated chemical or other fluid(Q_(chem)) (e.g., NaCl in the example of FIG. 5) (step 606). Flowcontroller 102 can initially act as if the flow of NaCl will have littleeffect on the temperature of t_(T2). Therefore, the cold fluid flowcontroller can set t_(T)=t_(T2) and determine Q_(C) according to EQN 1,where Q_(T)=Q_(T1) and t_(T)=t_(T2) (step 608). Additionally, the coldfluid flow controller can set t_(SP)=t_(T) (also shown at 609).

When a trigger signal is received (step 610), the cold fluid flowcontroller can begin regulating fluid flow using Q_(C) as a flow rateset point, issue commands the hot fluid flow controller to regulate flowof the hot fluid and issue commands to the chemical flow controller tocontrol flow of the third fluid. The cold fluid flow controller can foradjust the flow of cold fluid according to fluid flow control schemesknown in the art, including but not limited to differential controlschemes, integral control schemes, proportional integral controlschemes, proportional integral differential, or fuzzy logic controlschemes. If the fluid flow of cold water is greater than the fluid flowset point, cold fluid flow controller can decrease the flow rate (step616), if the fluid flow of cold water is less than the fluid flow setpoint (step 618), the cold fluid flow controller can increase the flowrate, and if the cold fluid flow rate equals the set point (within anacceptable system tolerance), the cold fluid flow controller canmaintain the flow rate (step 620). Thus, the cold fluid flow controllercan adjust the flow rate of cold fluid based on the cold fluid flow rateset point Q_(C).

The cold fluid flow controller can also receive the temperature of themixed chemical from a temperature sensor downstream of the second mixer(e.g., can receive t_(M2) from temperature sensor 504 of FIG. 5) (step622). Using t_(M2), the cold fluid flow controller can calculate a newQ_(C) and t_(M2) as, for example, described in conjunction with FIG. 5(step 638). Cold fluid flow controller can then perform steps 618-620using the new Q_(C) and pass the new t_(SP) to the hot fluid flowcontroller. According to one embodiment, Q_(C) and t_(SP) can becontinually updated as t_(M2) changes.

As shown in FIG. 6B the hot fluid flow controller, can adjust the flowrate of the hot fluid based on the temperature of the mixed fluid(t_(M1)) and the mixed fluid set point (t_(SP)). The temperature of themixed fluid can be received either directly from a temperature sensor orfrom the cold fluid flow controller. Hot water flow controller 104receives the initial temperature set point t_(SP) (step 623). If t_(M1)is greater than t_(SP), the hot fluid flow controller decreases the flowrate of fluid (step 624), if t_(M1) is less than t_(SP), the hot fluidflow controller increases the flow rate of the hot fluid (step 626) andif t_(M1) is equal to t_(SP) (within acceptable system tolerances), thehot fluid flow controller maintains the flow rate of hot fluid (step628). The hot fluid flow controller can receive the new temperature setpoint at step 629 and perform steps 624-628 accordingly.

The chemical flow controller can similarly adjust the flow of theadditional fluid (e.g., concentrated NaCl) based on Q_(chem). If thefluid flow of the concentrated chemical (or other fluid) is greater thanthe Q_(chem), chemical flow controller can decrease the flow rate (step630), if the fluid flow of the concentrated chemical is less thanQ_(chem) (step 632), the cold fluid flow controller can increase theflow rate, and if the concentrated chemical flow rate equals the setpoint (within an acceptable system tolerance), the chemical flowcontroller can maintain the flow rate (step 634). Thus, the chemicalflow controller can adjust the flow rate of concentrated chemical basedon the cold fluid flow rate set point Q_(chem).

Additionally, the chemical flow controller can receive a measurement ofconductivity of the mixed chemical (step 640). Using the conductivity,the flow controller can adjust the concentration of chemical added atthe second mixer. If the conductivity indicates that the mixed chemicalis too concentrated, the flow controller can decrease the concentrationof concentrated chemical (step 642). If the conductivity sensorindicates that the mixed chemical is too dilute, the flow controller canincrease the concentration of the concentrated chemical added to theDIW. Otherwise, the concentration can be unchanged (step 646).

The flow charts of FIGS. 6A-6C represent one example embodiment of thepresent invention. However, it should be understood, that the steps ofFIGS. 6A-6C can be repeated as needed or desired and can be performed indifferent orders. Moreover, the steps implemented at each flowcontroller can be performed in parallel. While, in FIGS. 6A-6C, the coldwater flow controller is responsible for calculating various parametersand asserting set points to the hot water flow controller and chemicalflow controller, the steps of FIGS. 6A-6C can be otherwise distributedto the flow controllers. Additionally, the roles of the hot water andcold water flow controllers can be reversed such that the hot water flowcontroller controls flow based on a flow rate set point and the coldwater flow controller controls flow based on a temperature set point.

As discussed above, the various flow controllers can control the flow offluids to the mixers, the mixers (e.g., mixer 106 and mixer 312), whichcan optionally be static mixers. FIGS. 7A-7F provide diagrammaticrepresentations of one embodiment of a static mixer assembly 700 and itscomponents. Referring to FIG. 7A, static mixer assembly 700 includes amixer housing 702, an inlet assembly 704 and an outlet assembly 706.Inlet assembly 704 includes two inlets, inlet 708 and inlet 710. Theseinlets can be coupled to fluid supply lines that lead from upstream flowcontrollers. For example, inlet 708 can receive hot DIW from hot DIWflow controller 102 and inlet 710 can receive cold DIW from cold DIWflow controller 104. In the example shown in FIG. 7A, inlet assembly 704has male threaded sections 712 and 714 to connect to inlet supply lines.Similarly, outlet assembly 706 has male threaded section 716 to connectto an outlet line.

FIG. 7B is a partial cutaway of mixer assembly 700 and illustrates aflow path 718 defined through mixer housing 702 from inlet assembly 704to outlet assembly 706. Thus, fluids entering inlet 708 and inlet 710 ofinlet assembly 704 exit a common outlet. FIG. 7B further illustratesthat inlet assembly 704 can include a male threaded portion 719 andoutlet assembly 706 can include a male threaded portion 720 to couple tomixer housing 702, which has corresponding female threaded portions.

FIG. 7C illustrates another partial cutaway of mixer assembly 700. Asshown in FIG. 7C, mixer assembly 700, according to one embodiment of thepresent invention includes a mixer disk 722 that acts as a static mixer.In the embodiment of FIG. 7C, mixer disk 722 is located in mixer housing702 at the outlet side of inlet assembly 704. Mixer disk 722 can includea seating flange 724 that rests in a corresponding annular ring ofhousing assembly 702. Seating flange 724, working in concert with theannular ring as a tongue and groove fitting, can ensure proper seatingof mixer disk 722 in mixer housing 702. Additionally, mixer disk 722 caninclude an annular ring 726 on its upstream side that receives a flangeon the outlet side of inlet assembly 704. This also aids in properseating of mixer disk 722.

By way of example, but not limitation, inlet assembly 704 and outletassembly 706 are configured to connect to ⅜ inch O.D. tubing with a 0.25inch bore and flow path 718 has a 0.21 inch diameter. Moreover, thevarious components of mixer assembly 700, according to one embodiment,can be machined or molded from Teflon or modified Teflon.

FIG. 7D is a diagrammatic representation of one embodiment of mixer disk722 showing one embodiment of the upstream side. Mixer disk 722,according to one embodiment of the present invention, includes an outersection 728 defined by an outer surface 729 at an outer circumferenceand an inner surface 730 at an inner circumference 731. Additionally,outer section 728 can include an annular ring 726 that receives, asdiscussed above, a flange on the outlet side of inlet assembly 704 toaid in seating.

In the embodiment of FIG. 7D, an inner flange 732 projects inwardly frominner surface 730 with an inner flange surface 733 that defines a flowpassage. Two radially opposed mixing tabs (tab 736 and 738) furtherproject inwardly towards each other. According to the preferredembodiment, mixing tab 736 and 738 do not touch, but have a small gapbetween them to leave the center of the flow passage unobstructed.Mixing tab 736 and mixing tab 738 can have downstream surfaces extendingapproximately normal to inner flange surface 733 and inclined upstreamsurfaces such that the mixing tabs are thinner near the center of theflow passage and wider proximate to inner flange 732. According to oneembodiment, the upstream surfaces of mixing tabs 736 and 738 areinclined approximately fifteen degrees.

Mixer disk 722 can further include an alignment notch 740 to align mixerdisk 722 in mixer assembly housing 702. Alignment notch 740 can matewith a corresponding protrusion in mixer assembly housing 702 to alignmixer disk 722 to have a particular orientation. For example, mixer disk722 can be aligned such that mixing tabs are oriented in particulardirection.

FIG. 7E is a diagrammatic representation of mixer disk 722 from anupstream view. By way of example, but not limitation, the outer diameterof outer section 728 can be 0.55 inches, and the inner diameter 0.21inches. The inner diameter of inner flange 732 can further be 0.166inches. Each of mixing tabs 736 and 738 can extend inwardly 0.074 frominner flange 732 with a gap of 0.018 inches between the mixing tabs.Again, by way of example, annular groove 726 can have an outer diameterof 0.45 inches and a thickness of 0.029 inches. It should be noted thatthese dimensions are provided by way of example and not limitation andlarger or smaller mixing disks can be used. Additionally, the variousradii or other example dimensions can be differently proportionedrelative to each other.

FIG. 7F is a section view of one embodiment mixer disk 722 along line AAof FIG. 7E. In addition to the features discussed in conjunction withFIG. 7D, FIG. 7F illustrates seating flange 724. In this embodiment,seating flange 724 is an annular ring projecting from the downstreamside of mixer disk 722. It can also be noted from FIG. 7F that tabs 736and 738 can be wedge shaped with the upstream surface of each tabangling 15 degrees inward as it approaches the center of mixer disk 722.The downstream surface, on the other hand, remains perpendicular to theflow passage. The tabs can have other shapes and there can be more thantwo tabs, or a single tab. Additionally, the dimensions and angles shownin FIG. 7F are provided by way of example, but not limitation.

FIGS. 8A-8C provide diagrammatic representations of another embodimentof a mixer assembly. Referring to FIG. 8A, static mixer assembly 800includes a mixer housing 802, three inlet assemblies 804, 806 and 808 anoutlet assembly 810. Each of the inlet assemblies can include an inletconnected by a supply line to supply a fluid. Using the example of themixing system of FIG. 3, inlet assembly 804 includes an inlet throughwhich the mixed fluid (e.g., mixed DIW) can supplied (e.g., from mixer106 of FIG. 3) while inlet assemblies 806 and 808 include inlets throughwhich concentrated chemical can be provided by a chemical flowcontroller (e.g., chemical flow controller 310 of FIG. 3). In theexample shown in FIG. 8A, inlet assemblies 804, 806 and 808 have malethreaded sections 812, 814 and 816, respectively, to connect to inletsupply lines. Similarly, outlet assembly 810 has male threaded section818 to connect to an outlet line.

FIG. 8B is a partial cutaway of mixer assembly 800 and illustrates aflow path 820 defined through mixer housing 802 from inlet assembly 804to outlet assembly 810. Additionally, FIG. 8B illustrates fluid flowpaths 822 and 824 through inlet assemblies 806 and 808, respectively,which join with flow path 820. Thus, fluids entering inlet assembly 804,inlet assembly 806 and inlet assembly 808 exit a common outlet. FIG. 78further illustrates that inlet assembly 804 can include male threadedportion 824, inlet assembly 806 can include male threaded portion 826,inlet assembly 808 includes male threaded portion 828 and outletassembly 810 can include a male threaded portion 830 to couple to mixerhousing 802, which has corresponding female threaded portions.

FIG. 8C illustrates a cross sectional view of one embodiment of mixerassembly 800. As shown in FIG. 8C, mixer assembly 800, according to oneembodiment of the present invention, includes a mixer disk 832 that actsas a static mixer. In the embodiment of FIG. 8C, mixer disk 832 islocated in mixer housing 802 at the outlet side of inlet assembly 804.Mixer disk 832 can include a seating flange 834 that rests in acorresponding annular ring of housing assembly 802. Seating flange 834,working in concert with the annular ring as a tongue and groove fitting,can ensure proper seating of mixer disk 832 in mixer housing 802.Additionally, mixer disk 832 can include an annular ring 836 thatreceives a flange on the outlet side of inlet assembly 804. This alsoaids in proper seating of mixer disk 832.

FIG. 8C also illustrates that flow passages 822 and 824 intersect withflow passage 820 downstream of mixer disk 832. Consequently, in a mixingsystem such as that depicted in FIG. 3, the concentrated chemical isintroduced downstream of mixing disk 822.

By way of example, but not limitation, inlet assembly 804, inletassembly 806, inlet assembly 808 and outlet assembly 810 are configuredto connect to ⅜ inch O.D. tubing with a 0.25 inch bore. By way ofexample, but not limitation, flow path 218 has a 0.21 inch diameter. Thevarious components of mixer assembly 800, according to one embodiment,can be machined or molded from Teflon or modified Teflon. Mixer disk 822can be similar or identical to mixer disk 722 of FIGS. 7D-7F. Mixingdisk 822 can be aligned (e.g. using the alignment notch) such that thetabs of mixing disk 822 are aligned over flow passage 822 and flowpassage 824.

As described above, embodiments of the present invention can provide afluid mixing system that utilizes various flow controllers (e.g., hotDIW controller 102, cold DIW controller 104 and chemical flow controller310). According to various embodiments, one of the flow controllers canact as a master controller that communicates set points to the otherflow controllers. Thus, the master flow controller is preferably capableof asserting multiple set points.

Many existing flow controllers receive set points as analogvoltages/current. Typically, this requires the use of multiple analogsources to provide set points to different flow controllers. However, aparticular flow controller may only have one or a limited number ofanalog ports available. This limits the number of slave flow controllersto which a particular master flow controller can assert set points.Embodiments of the present invention reduce or eliminate thedeficiencies associated with having a limited number of analog ports byproviding for multiplexing of analog set points on a particular analogcommunications link.

FIG. 9 is a diagrammatic representation of one embodiment of a system900 for multiplexing analog set points. System 900 includes an analogsignal source 902 connected to multiple slave devices 904 a-904 d via ananalog communications link 906 and one or more parallel digitalcommunications links 908. Analog signal source 902 can be a flowcontroller, such as an OptiChem P1200 produced by Mykrolis, Inc. ofBillerica, Mass. (now part of Entegris Corporation of Chaska, Minn.).Similarly, devices 904 a-904 d can also be OptiChem P1200 flowcontrollers. In other words, one flow controller, acting as analogsignal source 902 can act as a master device to other flow controllers.It should be noted, however, that analog signal source 902 can be anydevice capable of asserting an analog set point and devices 904 a-904 dcan be any devices capable of receiving analog set points.

Analog signal source 902 outputs an analog signal including set pointsfor multiple slave devices on analog communications link 906. Digitalcommunications links 908 a-908 d can carry set point indicator signalsto each of slave devices 904 a-904 d. It should be noted that thedigital communications links can be separate busses or the same busarbitrated to send a digital signal to a particular slave device 904. Aset point indicator signal for a particular slave device indicates thatthe analog signal is indicating the set point for that slave device.When a particular slave device 904 receives an indication that theanalog signal is specifying the set point for that device, theparticular slave device 904 can read its set point from the analogsignal. Using the set point indicator signals to indicate when setpoints for particular devices are being asserted on an analog lineallows multiple analog set points to be multiplexed on a single analogbus 906.

In FIG. 9, the analog set point signal and set point indicator signalsare illustrated as coming from the same master device. However, in otherembodiments of the present invention, the analog set point signal andset point indicator signals can be generated at distributed devices.

FIG. 10 illustrates one embodiment of a an analog set point signal 1000asserted by analog signal source 902, a set point indicator 1002 signalfor slave device 904 a a set point indicator signal 1004 for slavedevice 904 b, a set point indicator signal 1006 for slave device 904 cand a set point indicator signal 1008 for slave device 904 d. Accordingto the embodiment illustrated in FIG. 10, analog set point signal 1000can have voltages/current between 0% and 100% of a full scale value,whereas the set point indicator signals are either high or low (e.g.,cycling between +/−3.3 volts or other voltage values or other valuesindicating a setpoint).

In the example of FIG. 10, four analog set points are multiplexed intoanalog signal 1000. For time period t1 the set point is 45% of fullscale; for time period t2, the set point is 62% of full scale; for timeperiod t3, the set point is 30% of full scale; and for time period t4,the set point is 78% of full scale.

The analog set point values may have different meanings for the variousslave devices. For example, the analog set point may correspond to apressure at slave device 904 a, but a pump motor speed at slave device904 b. Thus, the analog set point signal can multiplex analog set pointsfor a variety of purposes.

During at least part of time period t1, set point indicator signal 1002changes states from high to low (shown at 1010) indicating that slavedevice 904 a should use the 45% of full scale value as its set point.Slave device 904 a can continue to use this set point value until theset point indicator signal indicates that it should read a new set pointfrom the analog set point signal 1000. Thus, slave device 904 a cancontinue to use the 45% of full scale set point even though the value ofthe analog signal is changing.

Similarly, set point indicator signal 1004 indicates that slave device904 b should use the 62% of full scale as its set point (shown at 1012),set point indicator signal 1006 indicates that slave device 904 c shoulduse the 3.0% of full scale as its set point (shown at 1014) and setpoint indicator signal 1008 indicates that slave device 904 d should usethe 78% of full scale as its set point (shown at 1016).

The signal timings provided in FIG. 10 are provided by way of exampleand any suitable scheme for indicating to a slave device when the analogsignal is carrying the set point for that device can be utilized. Forexample, the set point indicator signal can change states (e.g., fromlow to high, from high to low or undergo other state change) when theslave device should begin reading its set point from the analog setpoint signal and change states again when the slave device should stopreading its set point from the analog set point signal. Additionally,the set point indicator can be sent to the slave devices in a variety ofmanners, including as part of a data stream, an interrupt or in anothermanner.

According to another embodiment of the present invention, the set pointindicator signal can be asserted on multiple digital lines. FIG. 11 is adiagrammatic representation of one embodiment of a system 1100 formultiplexing analog set points. System 1100 includes an analog signalsource 1102 connected to multiple slave devices 1104 a-1104 d via ananalog communications link 1106 and a digital bus 1107. Digital bus 1107is connected to slave devices 1104 a-1104 d at 1108 a-1108 drespectively. Digital bus 1107 can include any number of lines forcarrying signals to slave devices 1104 a-1104 d. In the example of FIG.11, digital bus has three signaling lines. Analog signal source 1102 canbe a flow controller, such as an OptiChem P1200 produced by Mykrolis,Inc. of Billerica, Mass. (now part of Entegris Corporation of Chaska,Minn.). Similarly, devices 1104 a-1104 d can also be OptiChem P1200 flowcontrollers. In other words, one flow controller, acting as analogsignal source 1102 can act as a master device to other flow controllers.It should be noted, however, that analog signal source 1102 can be anydevice capable of asserting an analog set point and devices 1104 a-1104d can be any devices capable of receiving analog set points.

Analog signal source 1102 outputs an analog signal including set pointsfor multiple slave devices on analog communications link 1106. Digitalbus 1107 can carry set point indicator signals to each of slave devices1104 a-1104 d. A set point indicator signal for a particular slavedevice indicates that the analog signal is indicating the set point forthat slave device. The set point indicator signal for a particular slavedevice 1104 can be asserted as multiple bits on bus 1107. For example,the set point indicator for slave device 1104 d can be bits asserted onthe second and third signaling lines of bus 1107 (e.g., 011). When aparticular slave device 1104 receives an indication that the analogsignal is specifying the set point for that device, the particular slavedevice 1104 can read its set point from the analog signal. Implementinga binary weighted system for each of the digital select line extends thecapabilities of the master without increasing the number of digitalsetpoint indicator lines.

In FIG. 11, the analog set point signal and set point indicator signalsare illustrated as coming from the same master device. However, in otherembodiments of the present invention, the analog set point signal andset point indicator signals can be generated at distributed devices.

FIG. 12 illustrates one embodiment of a an analog set point signal 1200asserted by analog signal source 1102, and digital signals for providingsetpoint indicators. According to the embodiment illustrated in FIG. 12,analog set point signal 1200 can have voltages/current between 0% and100% of a full scale value, whereas the set point indicator signals areeither high or low (e.g., cycling between +/−3.3 volts or other voltagevalues or other values indicating a setpoint).

In the example of FIG. 12, four analog set points are multiplexed intoanalog signal 1300. For time period t1 the set point is 45% of fullscale; for time period t2, the set point is 62% of full scale; for timeperiod t3, the set point is 30% of full scale; and for time period t4,the set point is 78% of full scale.

The analog set point values may have different meanings for the variousslave devices. For example, the analog set point may correspond to apressure at slave device 1104 a, but a pump motor speed at slave device1104 b. Thus, the analog set point signal can multiplex analog setpoints for a variety of purposes.

During at least part of time period t1, set point signal 1202 changesstates from high to low (shown at 1210) indicating that slave device1104 a should use the 45% of full scale value as its set point. Slavedevice 1104 a can continue to use this set point value until the setpoint indicator signal indicates that it should read a new set pointfrom the analog set point signal 1200. Thus, slave device 1104 a cancontinue to use the 45% of full scale set point even though the value ofthe analog signal is changing.

Similarly, signal 1204 indicates that slave device 1104 b should use the62% of full scale as its set point (shown at 1212), signal 1206indicates that slave device 1104 c should use the 30% of full scale asits set point (shown at 1314). In time t₄, signals 1204 and 1206 asserta bit (shown at 1216 and 1218), indicating that slave device 1104 dshould use the 78% of full scale as its set point (i.e., multipledigital lines are used to send the setpoint indicator to slave device1104 d). Thus, three set point indicator lines are used to indicatesetpoint to four slave devices. Using a binary scheme up to 7 slavedevices can be supported (2^(n)−1, where n is the number of setpointindicator lines) with one signal state reserved for the case in which nosetpoint is being asserted for a device.

The signal timings provided in FIG. 12 are provided by way of exampleand any suitable scheme for indicating to a slave device when the analogsignal is carrying the set point for that device can be utilized. Forexample, the set point indicator signal can change states (e.g., fromlow to high, from high to low or undergo other state change) when theslave device should begin reading its set point from the analog setpoint signal and change states again when the slave device should stopreading its set point from the analog set point signal. Additionally,the set point indicator can be sent to the slave devices in a variety ofmanners, including as part of a data stream, an interrupt or in anothermanner.

FIG. 13 is a flow chart illustrating one embodiment of a method formultiplexing analog set points. The flow chart is divided into twosections for the master and slave device. The methodology of FIG. 13 canbe implemented, for example, by execution of computer instructions atthe master, slave or other devices.

According to one embodiment, an analog signal source generates an analogsignal representing multiple set points (step 1302). Put another way,multiple analog set points are multiplexed in the analog signal. Themaster device communicates the analog signal to the slave devices. Whenthe set point for a particular slave device is being transmitted via theanalog signal, the master device can send a set point indicator to thatslave device (step 1304). For example, the master device can use asignal on a digital bus (e.g., by changing the state of a line or lineson the bus) to indicate to a particular slave device that its set pointis being asserted on the analog line. The routine can continue until apredefined event occurs to end the routine.

The slave device can receive the analog set point signal (step 1306).When the slave device receives a set point indicator indicating that theanalog set point signal is asserting that slave device's set point(e.g., as determined at 1308), the slave device can save the value ofthe analog set point signal and store the signal as its set point (step1310). This routine can continue until a predefined event occurs to endthe routine. Additionally, the steps of FIG. 13 can be repeated asneeded or desired.

While the present invention has been described with reference toparticular embodiments, it should be understood that the embodiments areillustrative and that the scope of the invention is not limited to theseembodiments. Many variations, modifications, additions and improvementsto the embodiments described above are possible. It is contemplated thatthese variations, modifications, additions and improvements fall withinthe scope of the invention as detailed in the following claims.

1. A fluid mixing system comprising: a first flow controller to controlthe flow of a first fluid; a second flow controller to control the flowa second fluid; a first mixer in fluid communication with and downstreamof the first flow controller and second flow controller to mix the firstand second fluid to produce a first mixed fluid; a first temperaturesensor downstream of the first mixer to measure the temperature of thefirst mixed fluid; wherein the first flow controller is configured toregulate the flow of the first fluid using a first fluid target flowrate; and the second flow controller is configured to regulate the flowof the second fluid based on a temperature setpoint and temperature ofthe first mixed fluid.
 2. The fluid mixing system of claim 1, furthercomprising: a first fluid temperature sensor to measure a first fluidtemperature; and a second fluid temperature sensor to measure a secondfluid temperature; wherein the first flow controller is furtherconfigured to determine the first fluid target flow rate using the firstfluid temperature, the second fluid temperature, a target temperature ofthe first mixed fluid and a first mixed fluid target flow rate.
 3. Thefluid mixing system of claim 2, wherein the first flow controller isconfigured to provide the temperature setpoint to the second flowcontroller.
 4. The fluid mixing system of claim 2, wherein thetemperature setpoint is the target temperature for the first mixedfluid.
 5. The fluid mixing system of claim 4, wherein the first fluid iscold de-ionized water and the second fluid is hot de-ionized water. 6.The fluid mixing system of claim 1, wherein the first mixer is a staticmixer.
 7. The fluid mixing system of claim 1, further comprising: asecond mixer downstream of the first mixer; and a third flow controllerto regulate the flow of a third fluid, wherein the third fluid is addedto the first mixed fluid to create a second mixed fluid.
 8. The fluidmixing system of claim 8, wherein the third flow controller regulatesthe flow of the third fluid based on a third fluid target flow rate. 9.The fluid mixing system of claim 7, wherein the first fluid isde-ionized water, the second fluid is de-ionized water and the thirdfluid is a concentrated chemical.
 10. The fluid mixing system of claim9, wherein the first fluid is cold de-ionized water and the second fluidis hot de-ionized water.
 11. The fluid mixing system of claim 9, whereinthe second mixed fluid is a diluted solution of the concentratedchemical.
 12. The fluid mixing system of claim 7, further comprising asecond temperature sensor downstream of the second mixer to measure atemperature of the second mixed fluid.
 13. The fluid mixing system ofclaim 12, wherein the temperature setpoint is adjusted based on thetemperature of the second mixed fluid.
 14. The fluid mixing system ofclaim 12, wherein the first controller is configured to: receive thetemperature of the second mixed fluid; calculate a new first fluidtarget flow rate using the temperature of the second mixed fluid;calculate a new temperature setpoint using the temperature of the secondmixed fluid; and provide the new temperature setpoint to the secondcontroller.
 15. The fluid mixing system of claim 12, wherein the firstcontroller is configured to determine the third fluid target flow rateand first fluid target flow rate based on a second mixed fluid targetflow rate and target mix ratio of the second mixed fluid.
 16. The fluidmixing system of claim 12, further comprising a conductivity sensor tomeasure the conductivity of the second mixed fluid.
 17. The fluid mixingsystem of claim 16, wherein the third flow controller is operable toadjust the concentration of the third fluid based on the conductivity ofthe second mixed fluid.
 18. A fluid mixing method comprising: providinga first fluid and second fluid to a first mixer; mixing the first fluidand second fluid at the first mixer to create a first mixed fluid;measuring the temperature of the first mixed fluid; regulating the flowof the first fluid to the mixer based on a first fluid target flow rate;and regulating the flow of the second fluid to the mixer based on thetemperature of the first mixed fluid and a temperature setpoint.
 19. Thefluid mixing method of claim 18, further comprising: determining thetarget flow rate of the first fluid based on a first fluid temperature,a second fluid temperature, a target temperature of the first mixedfluid and a first mixed fluid target flow rate.
 20. The fluid mixingmethod of claim 18, further comprising: determining the temperaturesetpoint at a first flow controller that regulates the flow of the firstfluid; and providing the temperature setpoint to a second flowcontroller that regulates the flow of the second fluid.
 21. The fluidmixing method of claim 20, further comprising setting the temperaturesetpoint equal to a target temperature for the first mixed fluid. 22.The fluid mixing method of claim 18, further comprising: mixing thefirst mixed fluid with a third fluid at a second mixer to create asecond mixed fluid; and measuring the temperature of the second mixedfluid.
 23. The fluid mixing method of claim 22, further comprisingdetermining a first mixed fluid target flow rate based on a second mixedfluid target flow rate of and a target mix ratio of the second mixedfluid.
 24. The fluid mixing method of claim 23, further comprisingadjusting the temperature setpoint based on the temperature of thesecond mixed fluid.
 25. The fluid mixing method of claim 24, furthercomprising adjusting the first fluid target flow rate based on thetemperature of the second mixed fluid.
 26. A fluid mixing systemcomprising: a hot fluid flow controller to control the flow of a hotfluid; a cold fluid flow controller to control the flow of a cold fluid;a first static mixer downstream of the first hot fluid flow controllerand the cold fluid flow controller to receive the hot fluid, receive thecold fluid and mix the hot and cold fluids to create a mixed fluid; amixed fluid temperature sensor to determine the temperature of the mixedfluid; a chemical flow controller to control the flow of a chemical; asecond static mixer downstream of the chemical flow controller and thefirst static mixer to receive the mixed fluid, receive the chemical andmix the mixed fluid and the chemical to create a dilute chemical; and achemical temperature sensor to measure the temperature of the dilutechemical; wherein the cold fluid flow controller: controls the flow ofthe cold fluid based on a cold fluid target flow rate; communicates atemperature setpoint to the hot fluid flow controller; the hot fluidflow controller regulates the flow rate of the hot fluid based on thetemperature setpoint and temperature of the mixed fluid; and thechemical flow controller controls the flow of the chemical based on atarget chemical flow rate.
 27. The fluid mixing system of claim 26,wherein the cold fluid flow controller determines a target mixed fluidflow rate and the target chemical flow rate based on a target dilutedchemical flow rate and target mix ratio.
 28. The fluid mixing system ofclaim 27, wherein the cold fluid flow controller determines the coldfluid target flow rate based on a cold fluid temperature, a hot fluidtemperature, the mixed fluid target flow rate and a target temperature.29. The fluid mixing system of claim 28, wherein the target temperatureis the target temperature of the diluted chemical.
 30. The fluid mixingsystem of claim 28, wherein the target temperature is the targettemperature of the mixed fluid.
 31. The fluid mixing system of claim 28,wherein the cold fluid flow controller adjusts the temperature setpointand cold fluid target flow rate based on the temperature of the dilutechemical.
 32. The fluid mixing system of claim 26, further comprising aconductivity sensor downstream of the second static mixer to measure theconductivity of the dilute chemical.
 33. The fluid mixing system ofclaim 32, wherein the chemical flow controller adjusts the concentrationof the chemical supplied to the second static mixer based on theconductivity of the dilute chemical.